Electron discharge apparatus



' May l, 1945.

J. H. FREMLIN ELECTRON DISCHARGE APPARATUS Filed Nov. 27, 1940 Fig. I.

/NVEN T02 Patented May 1,' 1945A 2,314,810 ELacrnoN DISCHARGE APPARATUS .,Jolm' Beaver Fremlin, London W.C.2, England, as signor to International Standard Electric Corporation, New York, N. Y.

Application November 27, 1940, Serial No. 367,402 In Great Britain December 22, 1939 claims. (ci. 315-5) I This invention relates to electron discharge apparatus for operation at very high frequencies and has as one vof its objects to stabilise the resonant frequency of hollow resonators used in such apparatus and as another object to modulate the frequency of Vsuch resonators. l

.The features of the invention have particular application i-n electron discharge apparatus of the velocity-modulated type especially the apparatus disclosed in my Patent No. 2,320,860, issued June 1, 1943.

In accordance with -one part ofthe invention means are provided responsive to changes' in the dimensions or resonant frequency of a substantially closed hollow resonator for modifying the dimensions in a sense tending to maintain the resonant frequency constant. J

According to another part of the invention, there is provided means such as a piezoelectric crystal adapted when excited by a modulating voltage to modify the dimensions of a substantially closed hollow resonator and thereby to modulate the lnatural frequency.

On one aspect of the invention, different portions of the resonatorare constructed of conductive material having different temperature coeflicients of expansion so that the resonant frequency is substantially'independent of tempera-A ture.

An arrangement in accordance with this aspect is shown in Fig. 1 of the accompanying drawing.

Other aspects of the invention will hereinafter be pointed out or'will become apparent from a reading of the following specification in conjunction with the drawing included herewith. In said drawing- Fig. 1 is a section through a resonator arranged in accordance with'the said co-pending application; and Figs. 2, 3 and 4 are illustrative showings of embodiments in accordance with the invention.

The resonatorof Fig. 1 may a section of coaxial conductor transmission line short-circuited at its ends and is constituted by inner. and outer co-axial copper cylinders A and B connected together byl end-discs (not shown) and having Aa group of slots through the walls along a common diameter providing a passage for electrons focused in a beam from a cathode H to a col-` lecting anode F. The slots are provided with result of velocity modulation at the gap between D and E, yield up energy to the resonator. This unduly increasing the capacity between the cylinders A and B. Consequently variation of the length of this gap has a large effect upon the frequency of the resonator.

It is now proposed to make the ns C of Invar or other metal having a low thermal expansion, that is, having a-low temperature co-eiiicient of expansion and to connect them, at their outer ends only, to flanges L extending from `the cylinder A, the flanges L being of metal such as copper having higher thermal expansion, that is, having a higher temperature coefficient of expansion than age which varies in amplitude with changes in the ns C. When during` operationv of the .'discharge device the temperature of the resonator rises the radial dimensions of cylinders A and B increase tending to lower the resonant frequency. The copper flanges L=also increase in length, and the fins C which have relativelynegligble expansion are'drawn outwardly/"Thereby the ca.- pacity of the working gap is decreased and the decrease in frequency due to thermal expansionis partially or wholly compensated.

In another aspect of the invention a frequency-error-detector is employed to set up a control voltage or current for correcting'the resonant frequency of a resonator.

The error detector may comprise an auxiliary resonator loosely coupled to the mainv resonator and tuned to a frequency slightly different from the operative resonant frequency of the mainL resonator. From the auxiliary resonator a voltres'onant frequency of the main resonator is obtrainedv4 and this can be rectified and utilised to 7 vary continuously the dimensions of the main resonator in compensating sense.

Preferably the error detector comprises a pair of auxiliary resonators coupled to the mainresonatorand tuned respectively slightly above and below the voperative resonant frequency. YThe outputs of the auxiliary resonators are fed to ployed las error detectors should be of substan'l tially constant frequency. It is usually possible to maintain them at substantially constant temperature'but in any case they may be made of invar or the like copper-plated internally. The error detector in its preferred form may be used for example in the following ways.

The relays, for example grid-controlled gasdischarge cubes, operated by the error detector working gap is made as small as,4 possible without may control selectively the heating current to a pa'ir of coils or other resistances for the heating of bimetallic members coupled mechanically to a movable element for adjusting the capacity of the resonator. One arrangement is shown in Fig. 2 of the drawing where A, B, C, D, E comprise a resonator of the same form as in Fig. 1.

The ns C are slidable in the cylinder A and are carried by a rod fixed at its upper end and consisting of two lengths of biinetallic strip N welded together at M. Each strip has a heating coil P and they are arranged to bend in opposite directions. When the frequency of 'the resonator increases the auxiliary resonator tuned above the operative resonant frequency'supplies a Acurrent to its associated rectifier which triggers the gas discharge relay to supply heating current to the coil effective upon that bimetallic strip which opcrates to increase the working gap between fins C and D. Should the frequency of the resonator fall below its desired operative value the other auxiliary resonator is effectivev to decrease the gap to a sufcient degree to correct the frequency.

Another method is to feed the outputs of the A wave detectors or rectiers of the error detector to voltage amplifiers the outputs of which are applied to piezo-electric crystals the thickness-of which 'determines the capacity at the working gap. As shown in Fig.- 3 of the drawing silvercoated quartz plates Q are provided. Each quartz plate has one face fixed with respect to xed iins CI, DI while the other face carries or engages a pair f sliding ns C or D. When the thickness of one quartz plate is increased by applying to it the output of one voltage amplier the effective capacity is increased by the movement of the corresponding pair of fins C or D. 'The thickness t of the other may ibe decreased to decrease the effective capacity.

Methods of deriving from the two auxiliary resonators a. single 'diierential voltage for control purposes, as shown in Fig. 4, may be'employed using the principles adoptedfor example, in automatic frequency correction systems in radio receivers. The single differential voltage suitably amplified or the amplified -output of an error detector employing but one auxiliary resonator .may be applied to a single crystal or to each of a number of crystals mounted in some such way as that' described with reference to Fig.3.

The methods of frequency stabilisation described are applicable in various types of electron discharge apparatus using low loss hollow resonators or circuits of the tuned cavity type. Where two such resonators or circuits are involved stabilisation is useful in tending to prevent differences arising in the resonant frequencies dur' ing operation. In .any case frequency drift is highly undesirable'in the majority of applications of the apparatus.-

yIt will be apparent that those forms of frequency stabilisers which can operate rapidly and without lag under the control of a varying voltage, for example that described with reference to Fig.

3, can alternatively be employed for frequency the use of Rochelle salt crystals instead of quartz if the modulation frequency is not too great.

What is claimed is:

1. In an electron discharge apparatus' of the velocity modulated type a substantially closed hollow conductive bodyresonant at a very high frequency, said body including an adjustable element for changing the resonant frequency of said body, said adjustable element including bimetallic members to move said element, heating coil means for said bi-metallic members, means connected to the output of said body and responsive to a frequency greater than the frequency of said body, means connected to the output of said body and responsive to a frequency less than the frequency of said body, and rectifier means controlling said heating coil means in response to said first mentioned means to cause said adj ustable element to move in one sense and in response to said second mentioned means to move said element in a .sense opposed to said iirst sense.

2. In an electron discharge apparatus of the velocity modulatedv type a substantially closed hollow conductive body resonant to a very high frequency, having inward extensions forming an electron passage through said body, at least one of said extensions being arranged slidably in said body for changing the resonant frequency of said body, said slidable extension engaging a, piezoelectric crystal, means connected to the output of said body and responsive to a frequency greater than the frequency of said body, means connected to the output of said body and responsive to a frequency less than the frequency of said body, said crystal being connected with vthe output `of said rectifier means, said rectier means being responsive to said first mentioned means to cause said slidable extension to move in one sense and responsive to said second Vmentionedmeans to move said slidable extension in a sense opposed to said first sense.

`3. In an electron discharge apparatus of the velocity modulated type, including a, substantially `closed hollow conductive body resonant to a very high frequency having inward extensions forming an electron passage through said body, at least one of said extensions being arranged slidably inv said body, frequency comparison means to produce control energy corresponding to deviations from said frequency, control means comprising an integral control member, an electrically'rel sponsive body; for transforming electrical changes lint() dimensional changes, said electrically responsive body engaging said slidable extension to change the inward length thereof in accordance with dimensional changes of said electrically responsive body in response to said control energy and in a. sense tending to maintain the resonant frequency of said hollow conductive body constant. y,

4. In an electron discharge 'apparatus in accordance withclaim 3, in which Vsaid integral control member consists of a bi-metallic thermostat having an electrical heater for changing the dimension thereof .f

5. In an electron discharge apparatus in accordance with claim 3, in whichsaid integral control member consists of a. piezo-electrlccrystal having electrode connections for changing the dimensions thereof. i JOHN BEAVER PREMLIN. 

